Variable output transformer



y 1952 J. E. JONES ET AL 2,598,555

VARIABLE OUTPUT TRANSFORMER Original Filed July 2, 1948 Patented May 27,1952 VARIABLE OUTPUT TRANSFORMER Jesse E. Jones, Wauwatosa, and James B.Reeves,

Whitefish Bay, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis.,a corporation of Delaware Original application July 2, 1948, Serial No.36,718. Divided and this application April 20, 1951, Serial No. 222,026

2 Claims.

This invention relates to transformers and more particularly totransformers of the variable output type.

The present application is a division of our application Serial Number36,718, filed July 2, 1948, now Patent No. 2,571,454.

A primary object of the present invention is to provide a transformeraffording an output signal variable throughout a wide range, and

Another object is to provide a transformer of the aforementioned typehaving variable coupling means which is substantially frictionless andoperable without producing any retarding torque, whereby the couplingmeans will respond to a very small operating force such as may betransmitted through textile thread without undue strain thereon.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates a preferred embodiment of theinvention which will now be described, it being understood that theembodiment illustrated is susceptible of various modifications withoutdeparting from the scope of the appended claims.

In the drawings:

Figure 1, which is in part diagrammatic and in part schematic,illustrates a control system for motor-driven thread winding apparatusincorporating the invention;

Fig. 2 is a view in front elevation of a variable coupling transformershown schematically in Fig. l, and

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2.

Referring to Fig. 1, it shows a motor-driven thread winder comprising areel or bobbin It! on which a length of thread II is to be wound bymeans of a three phase alternating current motor I2 which drives bobbinIEI through a shaft I3. The thread II is shown as being supplied from aspool I4 which may here be assumed to be driven at a constant rotationalspeed through means not shown.

Idler rollers I5 and I6 are suitably placed in the path of thread I Ibetween spool I4 and bobbin ID to facilitate the formation of a loop orfestoon in thread I I which passes through a thread guide or eyelet I'Isecured to a tension arm I8 of a control device l9. Tension arm I8 isnon-rotatably secured to a shaft 20 of control device I9 and is providedwith a weight 2| which may be variously positioned thereon to adjust theforce exerted through the eyelet I! on thread I I.

The motor I2 is shown as being of the squirrel cage type, its primarybeing provided with supply terminals T T and T which are respectivelyconnected to supply lines L L and L of a three phase alternating currentsource; terminal T being connected to supply line L in series with aresistor 22. Motor I2 may be any suitable three phase alternatingcurrent motor having high secondary resistance, a motor of the so-calledtorque type being preferred.

A gas filled triode tube 23 is connected at its anode 23 to terminal 1'of motor I2 and at its cathode 23 to terminal T of said motor. Tube 23is provided with a control grid 23 which is connected to one end of acoil 24 of control device I9 through a resistor 25 and a rectifier 26. Acapacitor 21 and a resistor 28 are connected in parallel between thecathode 23 of tube 23 and the interconnnection between the resistor 25and rectifier 26, whereas a point common to cathode 23 resistor 28 andcapacitor 21 is connected to the end of coil 24 opposite the endaforementioned. A second capacitor 29 connected between cathode 23 andcontrol grid 23 of tube 23 is provided for by-passing transient andharmonic currents.

Control device I9 is also provided with a coil 30 which is connectedacross supply lines L and L and which has its longitudinal axis curvedconcentrically with shaft 20. An arm 3I is nonrotatably secured to shaft20 and is adapted to assume various angular positions in'rcsponse torotational movement of shaft 20 to vary the magnetic flux linking thecoils 24 and 30. A frame 32 (shown in broken lines) is provided tosupport the aforedescribed components of control device I9. The arm 3Iand frame 32 are preferably formed of magnetic material such as softsteel to provide a low reluctance path for the magnetic flux induced byenergization of coil 30'. A preferred form for control device I9 will behereinafter described in detail.

As will be apparent, the coil 30 will be energized whenever supply linesL and L are energized and as a result a voltage will be induced in thecoil 24. In the position of arm 3I depicted in Fig. 1, the maximumpossible magnetic coupling obtains between coils 24 and. 30 andconsequently the maximum possible voltage is induced in coil 24. Iftension arm I8 is'moved clockwise from its position depicted in Fig. 1,the arm M will be moved a corresponding amount in the same direction andthe magnetic coupling between coils 24 and 30 will be decreased. As aresult the voltage induced in coil 24 will be reduced in proportion tothe decrease in magnetic coupling. Movement of arm 3| upwardly beyond acertain point will not effect any appreciable reduction in the magneticcoupling, such point corresponding to minimum voltage induced in coil24. The action of control device I9 to produce a voltage varying invalue between a maximum and minimum in relation to mechanical movementof a part thereof is utilized to control the conduction of tube 23 forregulation of the speed of motor l2, as will now be explained.

Tube 23 is only capable of conduction when the potential polarities ofits anode 23 and cathode 23 are respectively positive and negative whichoccurs on alternate half cycles when the voltage at motor terminal T ispositive with respect to the voltage at terminal T of said motor. As afurther condition to conduction of tube 23 the potential of its controlgrid 23 must rise to a critical value, at which conduction is initiatedduring such half cycles. As will now be explained, the potentialattained by control grid 23 during each such half cycle is dependentupon the peak value of the induced voltage in coil 24 attained duringpreceding half cycle when tube 23 is non-conductive.

The coil 24 is so connected that on the half cycles when tube 23 isnon-conductive, the voltage induced in coil '24 will effect current flowthrough rectifier 26 and will charge capacitor 27 to a potentialcorresponding to the peak value of voltage induced in coil 23. As aresult the potential of control grid 23 will be made negative withrespect to the potential of cathode 23 in an amount corresponding to thepotential to which capacitor 21 is charged and in any event to an amountblocking conduction by tube 23. Unblocking of the tube is then dependentupon discharge of the capacitor through resistor 25, which dischargebegins as soon as the surge of current through the coil 24 reaches andpasses its peak. According to the charge of the capacitor and its rateof discharge unblocking of tube 23 is effected during the next halfcycle or may be continued throughout the next half cycle. In the latterevent the tube is rendered idle while in the former event the tubeconducts for part or all of the half cycle depending upon the movementat which the negative voltage impressed upon the control grid 23 isreduced sufficiently by discharge of the capacitor to permit the tube tobecome conductive with its anode and cathode respectively subjected topositive and negative voltages. When a condition of maximum magneticcoupling obtains in control device 19, capacitor 2'! will be charged tosuch a potential that its subsequent discharge will consume the nexthalf cycle, thus rendering'the tube idle during such half cycle.Reducing the degree of magnetic coupling in control device 19 will ofcourse reduce the potential to which capacitor 21 is charged, and if itbe reduced sufficiently, then the negative potential impressed upon thecontrol grid 23 will be reduced to permit conduction by tube 23 duringat least part of the half cycle following the half cycle during whichthe capacitor reserves its charge. A further reduction of magneticcoupling in control device l9 will result in initiation of conduction oftube '23 earlier in its conducting half cycles.

Conduction of tube 23 effects a single phase connection of motor l2,both its terminals T and T being connected to supply line L Consequentlywhile tube 23 conducts, the motor primary is afforded unbalancedexcitation. The resistor 22 normally effects a slight voltage unbalanceof the motor primary but the resistor need not be of a value such as toeffect more than a than it is fed from spool M.

negligible unbalance. Assuming that tube 23 conducts during portions ofalternate half cycles the motor periodically changes from a condition ofalmost balanced to unbalanced excitation which causes the speed of themotor to decrease. The greater the average current conducted by tube 23,the greater will be the reduction in speed of motor I2.

As will be understood, tension arm 18 acting through the eyelet l1,maintains the thread H under constant tension in its passage from spoolM to the bobbin H3 so long as a loop is maintained between rollers l5and it; the amount of tension being determined by the magnitude 3 andposition of weight 21 on arm 13. The diameter of bobbin H] willprogressively increase due to successive winding layers of thread I Iand the peripheral speed of bobbin ill will tend to increase withconsequent tendency to wind faster This causes the aforedescribed loopin thread H to progressively decrease in length as the bobbin itincreases in diameter. As a result tension arm "3 is progressively movedin the clockwise direction with consequent progressive reduction in themagnetic coupling between coils 24 and 39 of control device I9. Thus itwill be seen that the speed of motor 12 will be progressively reduced sothat the peripheral speed of bobbin It will be main- M, tainedsubstantially constant relative to the peripheral speed of spool I lwhich decreases as thread is unwound therefrom.

.Vhereas it has here been assumed that thread i l is unwound from aspool driven at a constant 3 rotational speed such a condition of threadsupon control device l9 can be best reduced by increasing the effectivelength of tension arm l8.

Referring to Figs. 2 and 3, they show a preferred form for controldevice Ii! which will now be described in detail.

The coils 2-5 and 35 are provided with individual carriers E l and Ellof a spool type, which are preferably formed of a non-magnetic materialsuch as a linen based Bakelite. Coil 38 is rigidly secured to plate 32by a plurality of attaching lugs 5 2 which are sheared from plate 32,peripherally about an end flange of carrier 36 and bent over said endflange. An opening extending axially through carrier 30 is provided tofreely accommodate the shaft which preferably is steel and on which thecoupling arm 3! is non-rotatably secured. Coil 24 is secured to plate 32in a spaced relation to coil 3i) by means of a screw which extendsthrough a central opening in carrier 2d and which takes into a threadedopening formed in plate 32.

An inverted U-shaped bearing bracket formed of a non-magnetic materialsuch as brass is secured to plate 32 in a straddling relation to coil bymeans of screws which extend through openings in oppositely dependingend portions of said bracket and take into threaded openings in plate32. The portion of bracket 35 overlying coil 3%] is provided with athreaded opening concentric with respect to shaft 21) to accommodate ascrew type bearing seat 35 for shaft 20. The end of seat 36 adjacentshaft 20 is provided with an inverted conical recess to partiallyaccommodate a small polished steel ball 31 which is also partiallyaccommodated in a corresponding recess formed in the adjacent end ofshaft 20. Seat 36 is slotted at its other end to facilitate itsadjustment relative to bracket 34 so that its recessed end may be movedtoward or away from shaft 20. A desired adjustment of seat 36 ismaintained by means of a nut 36 which has engagement with the threadedshank of seat 35 to be clamped against bracket 34 to lock seat 33 inadjusted position.

Shaft 2!), as aforedescribed, extends through the coil 30 and alsoextends through and beyond plate 32, the latter being provided with aclearance opening to accommodate said shaft. A ball bearing 38 is fittedon shaft 20 with a driving fit to afford radial bearing support for thelatter within a bearing housing 39 which is secured to plate 32oppositely of the coil 30. The housing 39 is secured to plate 32 by aplurality of screws 40 which pass through said housing marginallythereof and take into threaded openings formed in plate 32. Housing 39is suitably formed interiorly to tightly engage with ball bearing 38peripherally about the outer race of the latter and to restrain the sameand shaft 20 against any substantial axial movement. A clearance openingextending through the end wall of housing 39 is provided to accommodateshaft 20 which extends beyond said housing.

The coupling arm 3| is provided with a hub portion 3| which has anopening to accommodate with clearance a reduced threaded end por tion 20of shaft 20. Arm 3|, is non-rotatably secured to shaft 20 by a nut 4|threaded onto the portion 20 of shaft 20 to clamp said arm against anannular shoulder 20' formed on shaft 20. Arm 3| is provided with astraight portion 3| which is integrally connected to the hub 3| at oneend thereof and which merges at its other end with a portion 3| whichdepends perpendicularly toward the plate 32. The portion 3| 0 is soproportioned in length as to freely clear the carrier 24 upon angularmovement of arm 3|. Arm 3| is also provided with a circular segmentportion 3| which is integrally connected with the hub portion 3|; saidportion 3| affording limitation of angular movement of arm 3| byengagement of its radial sides with the portions of bracket 34 whichextend perpendicularly with respect to plate 32. Preferably, the portion3| is so proportioned as to afford balance of the arm 3| with respect toits pivotal axis.

Tension arm I8 is non-rotatably secured, in any preferred manner, to theportion of shaft 20 which extends beyond the housing 39. While tensionarm I8 is depicted in Figs. 2 and 3 as being mounted on shaft'MI incertain relation with respect to the portion 3| of coupling arm 3|, itmay be mounted in various relations to coupling arm 3| according to theparticular application of control device l9. Tension arm I 8 is depictedas having the open eyelet H as preferred thread engaging means, but aswill be apparent this may be replaced, if desired, by a roller when usedin connection with web materials or the like.

As will be apparent, when coupling arm 3| is in the position depicted infull lines in Fig. 2, the condition of maximum magnetic coupling betweencoils 24 and 30 is afforded and the voltage induced in coil 24 will beat a maximum. Conversely when coupling arm 3| is in the positiondepicted in broken lines in Fig. 2, a condition of minimum magneticcoupling between coils 24 and 30 is afforded and consequently thevoltage induced in coil 24 will be at a minimum. Accordingly, thevoltage induced in coil 24 can be varied between minimum and maximumvalues by variously positioning coupling arm 3| between the positionsaforedescribed.

As will be understood by those skilled in the art, coil 24 will have aconsiderably greater number of coil turns than coil 33 and the ratio ofcoil turns will depend upon the particular application and the circuitto which the coil 24 is connected.

We claim:

1. A transformer comprising a member formed of a material of lowmagnetic reluctance, a first coil for predetermined alternating currentexcitation mounted contiguously to said member, a second coil mountedcontiguously to said member in a manner such that its axis is parallelto the axis of the first coil and spaced therefrom by a distance atleast equal to the sum of the maximum radii of said coils, a shaftconcentric with said first coil and extending through said member,anti-friction bearing means supported on said member and affording saidshaft rotational bearing support, a member secured to the firstmentioned member and straddling said first coil and one end of saidshaft, anti-friction bearing means for said one end of said shaftcarried by the last mentioned member, and a second member formed of amaterial of low magnetic reluctance secured to said shaft in overlyingrelation to said first coil, said last mentioned member being soproportioned as to :be statically balanced about the axis of said shaftand being movable by rotation of said shaft into different relationswith said second coil to vary the magnetic coupling between said coilsthus to vary the potential induced in said second coil.-

2. In combination, a base member formed of a material of low magneticreluctance, a first coil for predetermined alternating currentexcitation mounted contiguously to said base member, a second coilmounted contiguously to said base member in a manner such that its axisis parallel to the axis of the first coil and spaced therefrom by adistance at least equal to the sum of the maximum radii of said coils, ashaft concentric with said first coil and extending through said member,anti-friction bearing means supported on said member and affording saidshaft rotational bearing support, a non-magnetic bracket member securedto said base member and straddling said first coil and one end of saidshaft, anti-friction bearing means for said one end of said shaftcarried by said bracket member, an arm member formed of a material oflow magnetic reluctance secured to said shaft in overlying relation tosaid first coil, said arm member being so proportioned as to bestatically balanced about the axis of said shaft and being movable byrotation of said shaft into different relations with said second coil tovary the magnetic coupling between said coils, and a tension armnon-rotatably secured to said shaft, said tension arm having means atits free end to accommodate and guide a thread and also having anadjustably positionable weight for varying the tension on said thread.

JESSE E. JONES. JAMES B. REEVES.

No references cited.

